Methyl siloxane polymers and method of preparation



Patented 4, 1948 UNITED STATE rm'rm smoxaxn rotmnns AND ME'rnon orrnsraaarron James Franklin Hyde, Corning, N. Y., assignor to CorningGlass Works, Corning, N. Y., a corporation or New York No Drawing.

Application September 9, 1946, Serial No. 695.803

4 Claims. (Cl. 260-607) This invention relates tonew compositions ofmatter, their preparation and uses and, more' particularly, to methylsilicon oxides and their preparation.

This application is a continuation-impart of my copending applicationSerial Number 503,159, filed September 20, 1943, and assigned to theassignee of the present invention.

Methyl silicon oxides or methyl siloxanes are compositions which containalternate silicon and oxygen atoms and methyl radicals attached tosilicon through a carbon atom. They may be prepared by hydrolysis of ahydrolyzable methylsubstituted silane and condensation of the hydrolysisproduct or by hydrolysis of a mixture of different hydrolyzablemethyl-substituted silanes and inter-condensation of the hydrolysisproducts. By hydrolyzable methyl-substituted silanes we mean methylderivatives of Sill-I4 which contain readily hydrolyzable radicals suchashalogens, amino groups, alkoxy, aroxy, acyloxy radicals, etc. Examplesof such compounds are methylsilicon trichloride, dimethylsilicondichloride, trimethylsilicon chloride, methyltriethoxysilane,dimethyldiethoxysilane, trimethylethoxysilane, etc. v

The methyl siloxanes hitherto prepared have contained mostly monoanddimethyl silicon units with some trimethyl' silicon units also beingpresent. They were liquids which when heated were readily converted togels or resinous solids. It is highly desirable for certain purposes,such as high altitude flying, to find a hydraulic fluid which is adaptedto function efiectively over a wide temperature range and particularlyat temperatures well below ---40 C. and preferably down to readycondensibility,

-60 C. Because of their? use of the above-mentioned 5 .methyl siloxanesas hydraulic fluids, damping fluids, etc., has been too hazardous fortheir adoption commercially. A liquid methyl sil-y oxane which isthermally stable and which possesses other properties such as lowsolidification temperature, low vapor pressure, relatively lowviscosity-temperature ccefiicient and high chemical stability would beextremely useful.

One of the objects of my invention is to provide a method of makingthermally-stable liquid methyl silicon oxide copolymers.

Another object of my invention is to provide a method oi makingthermally stable liquid methyl silicon oxide copolymers which are memomcm cm cm-si-o 1-0 1-03,

Ha Ha 41H:

polymers which have a low solidfication temperature, lowviscosity-temperature coeflicients and which do not set to a gel atelevated tem- 'peratures.

' The method of the present invention comprises hydrolyzing a mixtureconsisting of silanes of the formulae (CH1)2Sl(OR)2 and (0110381012.respectively in the presence of an alkali metal hydroxide where R is analkyl radical. 0f the alkali metal hydroxides, I prefer to employ-sodium and potassium hydroxides. The amount of the hydroxide present inthe hydrolysis medium must be such that the ratio of number of alkalimetal atoms to number of silicon atoms in v the mixture of silanes doesnot exceed 1 to 25. By this method it is possible to insure the maximumproduction of chain polymers end-blocked with trimethylsilicyl units.

The products prepared in accordance with the above methods consist ofthe structural units (i711; CH3 cm-si-o and cm-s i-o As prepared, by theexamples given, they consist of a random mixture of polymers of variouschain lengths, the individual members of which belong to the homologousseries represented by the formula where a: is an integer irom 1 toinfinity. However, owing to the :lifliculty of obtaining completehydrolysis and complete condensation there may be present a fewremaining unhydrolyzed ethoxy radicals, usually less than 1 for aboutsiloxane linkages, or the like, or some uncondensed hydroxyl groups,usually less than 1 for about 400 siloxane linkages, but not insufiicient amounts to impair the properties of the liquid products.

For many uses, particularly in fluid pressure operated devices, it ispreferred to use instead of the above mixtures of copolymers having arange of physical properties, an individual 00- polymer of the specieshaving the definite physical properties of a pure chemical compound.These may be obtained by isolation of the individual members from thehydrolysate of a mixture of (CHzlaSiX v and (CHzhSiXz which is preparedin such a manner.

as to be substantially completely hydrolyzed and free fromcyclicpolymers of the formula [(CHzJzSiO]: For a better understanding of myinvention,

reference should be had to the following example. 7

In a liter three-necked flash. fitted with a reflux condenser, agitatorand thermometer, were placed 1393 gms. (9.41 mol) of redistilled (CH3):SiiOEt): and 11l0 gms. (9.41 mol) of (CI-I2): SiOEt. To this solutionwas added 254 gms. (14.11 mol) of water containing 7.5 girls. of NaOH,(approximately 1 NaOH per 100 silicon atoms). This insured the formationof only straight chain polymers. The mixture was heated to 40 C. and thetemperature continued to rise for nearly an hour. After adding 50 cc.(20% excess) more water, the mixture was refluxed for two hours and thenallowed to stand overnight.

Alcohol was then distilled 011, until the temperature reached 100 C.1706.6 gms. of distillate 4 of from 125 to 215 C. at 0.125 mm.Refractionation of this distillate showed it to be composed of membersof the above series where X is 8 to 13 inclusive. That is, it consistedoi. copolymers of (CH3)3Si-O- with containing from 10 to 15 siliconatoms inclusive. The properties of these materials are shown in Table I,Section B; an undistilled residue of 39.1 gins. remained. This wastreated with decolorizing carbon and filtered to give the final residueas shown in the following Table I, Section C. Evidently, this residuecontained linear copolymers having more than 15 silicon atoms in the wascollected. (Theory 1430 gms.) This alcohol m l le, was poured into fourtimes its volume of water CH and an insoluble oil separated (457 gms.).The A insoluble fraction was added back to the copoly- 1)1SiO 1-0 suommer residuefrom the distillation and 555 cc. of $111 TABLE I Physicalproperties of trimethylsilicyl end blocked dimethyl silomane polymersAliitsoliutecviii Y n Specific Ref. Flash Goefl. 51 Exi gj B. P.,C.Gravit Index Point, pension to 5125" 5125 C. '1 100 (1x10 25 0 40 0 0.051.10 .7606 1.2143 15 1.50 1.04 291 .8182 1.3822 9s 1.451 iii as it; swimA 2153 9: 57 I 8873 1: 3922 245 1: 200 3. 24 12. 9004 l. 3940 272 1.i154 a. as 15. 40 9019 1. 3952 292 1. 130 119/05 4. 5s 19. 90 .9140 1.290:1 318 1.110

ice/0.5 111111..-. 5. 35 21.5 .9202 1.3973 350 1.078 152/115 mm..- 6.1028.3 9217 1. 3982 371 1.055 Section B 171 05 5. 85 as. 2 9284 1. 3990389 1. 034 7 195/05 mm.- 7.75 38.0 .9317 1.3998 406 1.016 ./0.5 a. 7044. a .9314 1. 4004 422 .999 222 05 111111---. 9.55 v 50.5 .9368 1.4010431 .992

BectionC Residue. 12.0 can .9454 1.4009 458 20% hydrochloric acid wasadded. The acid mixture was refluxed for two hours, and the silicon oilswere carefully washed with distilled water until neutral. The yield was1426 gins. (Theory 1469 gms.)

The oil was distilled in a fractionating column packed with glasshelices, first at atmospheric pressure, then at reduced pressure. Thefractions from the plateaus in the distillation curve werereiractionated and the properties of the pure siloxane polymers weredetermined. These are shown in the data of Table I, Section A, fromwhich it appears that the individual fractions are members of the series41-015MCH1)! 8H;

(CH2) 1Si0 containing from 3 to 9 silicon atoms inclusive.

The residue (178 gms.) from the fractional distillation was placed in aClaisen flask and distilled under high vacuum without fractionation.This gave a clear distillate distilling over a range Both the individualcopolymers and the copolymer mixtures of my invention are resistant tofurther polymerization at high temperatures in the presence of air. Thetable below gives the hours at 200 C. required to cause gelation ofdifferent copolymer mixtures of my invention both in the presence andabsence of an inhibitor (in the present case, 1% of p-amino-phenol).

TABLE 11 M01 Pro- Hours for Gelation at portions 200 C. in Air WithoutWith D1 111111111151- Inhibitor amines residual oil was cooled, filteredand found to have a viscosity of 58 centistokes at 25 0. and a flashpoint of 385 F. It would not freeze on rosure to temperatures of 50 to-60 C, A comparison of the viscosity of this liquid siloxane with a highgrade hydraulic fluid based on a petroleum oil is given in the tablebelow in Saybolt Universal seconds.

It will be seen from the above table that the viscosity change from 100to F. for the petroleum oil is nearly 11 times that of the methylsiloxane fluid.

The liquid methyl copolymers of my invention are eminently adapted to beused as damping fluids, hydraulic fluids, compass liquids, etc. They arecolorless, odorless, and inert physiologically and chemically. They arewithout corrosive eflect on metals and do not swell or deterioraterubber or synthetic rubber gasketing or tubing material. Liquids ofvarying intrinsic viscosity may be obtained to suit the individualapplication. The principal characteristics which adapt these polymericliquid methyl siloxanes to use in aircraft hydraulic fluids are theirlow rate of change of viscosity with change of temperaof silicon atomsin the mixture does not exceed 1 to 25, .and condensing'the methylsilicon hydrolysis product by dehydration.

2. The method which comprises hydrolyzing a mixture consisting ofdimethyldiethoxysilane and trimethylethoxysilane, which mixture containsat least one mol of the former per two mols ot the latter, by reactingthe mixture with water in amount in excess of that theoreticallyrequired to effect complete hydrolysis, in the presence of an alkalimetal hydroxide in such amount that the ratio of number of alkali metalatoms to the number, of silicon atoms in the mixture does not exceed 1to 25, and condensing the methyl silicon hydrolysis product bydehydration.

3. The method which comprises hydrolyzing a mixture consisting ofdimethyldiethoxysllane and trimethylethoxysilane, which mixture containsat least one mol of the former per two mols of the latter, "by reactingthe mixture with water in amount in excess of that theoreticallyrequired to efiect complete hydrolysis, in the presence of atoms doesnot exceed 1 to 25, and condensing the methyl silicon hydrolysis productby dehydration.

inertness to metals, rubber and other construction materials over thetemperature range used,

' and the high flash point and low vapor pressure R is an alkyl radical,which mixture contains at least one mol of the former per two mols ofthe latter, by reacting the mixture with waterin amount in excess ofthat theoretically. required to effect complete hydrolysis, saidhydrolysis being carried out in the presence of an alkali metalhydroxide in such amount that the ratio of 4. The method which comprisesheating a mixture consisting of dimethyldiethoxysilane andtrimethylethoxysilane, which mixture contains at least one mol of theformer per two mols of the latter, in the presence of aqueous sodiumhydroxide, the amount of water present being in excess of thattheoretically required to effect complete hydrolysis and the amount ofsodium hydroxide being such that the ratio of number of sodium atoms tonumber of silicon atoms does not exceed 1 to 25, and recovering themethyl silicon hydrolysis products, refluxing the methyl number ofalkali metal atoms to the number silicon hydrolysis. products in thepresence of aqueous hydrochloric acid, thereafter washing the productuntil neutral, and again recoverin the methyl silicon hydrolysisproducts.

JAMES FRANKLIN HYDE.

REFERENCES CITED The following references are of record in the flle ofthis patent:

UNITED STATES PATENTS

